As a polishing composition used in application for polishing a surface of a silicon substrate, polishing compositions containing water-soluble polymers have been known. Some water-soluble polymers have a function to reduce the haze level of a polished surface of a silicon substrate through stabilization of dispersion state of abrasive grains via adsorption onto abrasive grains, while some others have a function to be adsorbed onto a polished surface of a silicon substrate to improve the wettability of the polished surface.
In Patent Document 1, it is disclosed that a polishing composition containing a polyvinyl alcohol (PVA)-polyvinyl pyrrolidone (PVP) copolymer in which vinyl pyrrolidone (VP) has been graft-polymerized onto PVA is used in application for polishing a metal film formed on a substrate. According to the polishing composition of Patent Document 1, a high polishing rate can be attained, while maintaining a low etching rate upon the polishing of the metal film. In Patent Document 1, however, there is no disclosure of use of the polishing composition containing the PVA-PVP copolymer for polishing the silicon substrate.